Agreed would like to hear the reasoning. I always thought it was just each deers individual differences.
Somewhere I think I remember reading something about that trend. If I remember correctly, the author believed it had to do with buck age. But I'll have to try and find that article.
I would not expect age to be the factor causing this difference.
I got my buddy's and my shed collection together.. 3/4 of our sheds are cupped in. The rest are rounded on the bottom.
Of the ones that are rounded none of them have pedicle chipping (where it looks like the antler came off too early and brought a bit of the pedicle with it). Many of the cupped in ones are not smooth and have the chipping.
Someome with more sheds than I have should examine them and see if their are any trends with round vs cupped in. It may be related to when the shed is dropped in relation to when it would be completely ready to drop.